Vacuum furnace for dental laboratories



Nov. 5, 1963 M. J. KREMER VACUUM FURNACE FOR DENTAL LABORATORIES Filed Feb. 17, 1960 4 Sheets-Sheet 1 Q. INVENTOR.

I Md/(KE/fffi BY A TTOIP/VE Y Nov. 5, 1963 M. J. KREMER VACUUM FURNACE FOR DENTAL LABORATORIES 4 Sheets-Sheet 2 Filed Feb. 17, 1960 1 1/ I I l ww w 3 Nov. 5, 1963 M. J. KREMER 3, 0

VACUUM FURNACE FOR DENTAL LABORATORIES Filed Feb. 17, 1960 4 Sheets-Sheet 3 INVENTOR. A? K4 EMEQ Nov. 5, 1963 M. J. KREMER 3,109,911

' VACUUM FURNACE FOR DENTAL LABORATORIES Filed Feb. 17, 1960 4 Sheets-Sheet 4 Tlclb- 6 Buzzer kw)! wee/Ker duf/e/ ATTOR/VE Y United States Patent Marvin J. Kremer, Cedarhurst, N.Y., assignor to David Feinson, Inc New York, N.Y., a corporation of New York Filed Feb. 17, 1960, Ser. No. 9,320 4 Claims. (Cl. 2119-35) This invention relates to the art of firing dental articles, such as porcelain bridges and the like, employing improved apparatus to provide a custom service. In this way, a dentist may send articles to a laboratory equipped with a furnace device embodying the invention where such articles may be fired.

Furnaces embodying the invention are not intended to provide for making such articles on a production-line basis, such as in the fabrication of artificial teeth of standard size and types, but it is desired to provide for a more personal service for the dental profession.

Porcelain restorations fired pursuant to the invention have physical properties improved so that better impact and compressive strength, increased hardness and greater density are obtained. It has been found that restorations made in a furnace device embodying the invention are free of entrapped air which, under conventional firing, forms voids such as pockets and/or bubbles in the porcelain. Such voids within the product make it porous and disturb the natural reflection therefrom.

It is, therefore, an object of my invention to produce a vacuum furnace suitable for making improved dental objects, such as porcelain bridges, free from pits, pores, specks and bubbles.

Another object of my invention is to produce an improved furnace whereby dental articles, harder and denser than formerly, may be produced and which may be fin ished to a high glaze.

These and other objects and advantages will become apparent from the following detailed description when taken with the accompanying drawings. It will be understood that the drawings are for purposes of illustration and do not define the scope or limits of the invention, reference being had for the latter purpose to the appended claims.

In .the drawings, wherein like reference characters denote like parts in the several views:

FIGURE 1 is a perspective view of the exterior casing of a laboratory furnace device embodying the invention, showing the oven portion thereof removed from the housing portion of said device and the closure forsaid oven separated therefrom,

FIGURE 2 is a horizontal sectional view of the laboratory furnace device of FIGURE 1,

FIGURE 3 is a perspective view from the rear of the oven of the furnace device,

FIGURE 4 is a fragmentary perspective View from the rear of the vacuum chamber or housing of the furnace,

FIGURE 5 is a perspective view of the heating units of the oven, and

FEGURE 6 is a wiring diagram.

Referring to the drawings in detail, there is shown in FIGURE 1 a perspective of the exterior of the casing 12 of a furnace device embodying my invention and generally designated 11. This casing is formed by six generally rectangular walls, the bottom wall 13, side walls 14 and top wall 15 being generally imperforate or closed, while the rear wall 16 is for ventilation desirably formed as a lattice or of foraminous construction. The front wall 17 is formed with an opening 18 for the reception of the vacuum chamber or housing 19. This housing is desirably formed of steel and with walls of sufiicient thickness ice to withstand the atmospheric pressure thereon when exhausted to a relatively high vacuum, such as about 25 of mercury.

The portion of the front wall 17 to the left of the opening 18, as viewed in FIGURES l and 2, provides or serves as the instrument panel of the device. The housing or vacuum chamber 19, as well as the opening 18, is closable by a door 21, a rubber or other resilient gasket 22 being applied around the peripheral portion of the door so as to form a vacuum-tight seal with the edge portion of the housing 19 when said door is closed. The door 21 is desirably connected to the housing 19 by hinges or pivot means 23 for swinging about a normally vertical axis. The door 21 is provided with a latch bar 24 having a handle 25 and pivoted to the door as indicated at 26. The free end portion of the latch 24 is received in an upwardly opening flaring notch 27 provided by the keeper 28 outstanding from the housing 19. The inwardlydirected edge of said keeper desirably slopes downwardly and inwardly so that the latch 24 when received in the notch serves to wedge the door 21 to vacuum-tight position.

The front portion of the housing is desirably approxi mately flush with the outer surface of the front wall 17 of the casing, or projects only a slight distance therebeyond, as viewed in FIGURE 1. Near the bottom of the housing 19 are a pair of rails 29, desirably formed as angle irons with their lower flanges 31 disposed in generally horizontal coplanar relationship, as viewed most clearly in FIGURE 1, and their other flanges 32 extending approximately vertically to define therebetween a space which slidably receives the oven or muille proper 33 of the furnace device, while the latter rests on said lower flanges 31. The rails 29 desirably extend from front to rear of the housing 19, so as to provide for reception of the oven 33 thereon and for its slidable movement from front of the housing to a position near the rear wall thereof, and vice versa.

The oven 33 is desirably formed of steel and lined with refractory material 34, such as brick. Normally enclosed in said oven are electrical heating means, such as a number of heating units forming an assembly 35, each comprising a refractory slab or member in which resistance wire is embedded, said members being connected in series, as viewed in FIGURE 5 and, when in position, forming an enclosure open at front and rear in which the articles to be fired are received.

The relative size of the oven 33 with respect to the enclosing housing 19 is such that a space is normally provided therearound on all sides and at the top and bottom. The oven has a front opening 36, framed by an outstanding flange or boss 37 and, when in operation, is closed by a door or plug 38, desirably formed of ceramic or refractory material and having a boss 30 on its normally inner surface which fits the opening 36. A normally vertical flange 40 desirably projects from the front face of the closure 38. Disposed above and below the opening are angle irons 39 and 41, respectively, the lower one of which provides an outstanding flange 42 serving to engagingly support the closure 38 at its lower edge. The outstanding flange of the upper angle iron 39 may have a pair of apertures 50, one on either side of the flange 40, for viewing the top of the closure 38 when in place.

The oven 33 has a relatively small rear aperture 43 serving for the reception of a thermocouple 44. Said thermocouple is electrically connected through a reset switch 76 to contact prongs, 45 and 45, receivable in a corresponding socket device 47 mounted in the housing 19, for connection with a temperature indicator 51 mounted on the front wall 17 of the casing 12. The ends of the resistance wires of the heating units assembly 35 are respectively'connected to sockets 52 and 53 projecting rearwardly from the rear wall of the oven 33 and respectively connectible with prongs 54 and 55 mounted in the housing 19. Said prongs 54 and 55 project forwardly for reception in said sockets 52 and 53, simultaneously with the reception of the prongs 45 and 46 in the socket arrangement 47, upon rearward movement of the oven 33 in the housing 19.

The prongs 54 and 55 are electrically connected to prongs 56 and 57 projecting outwardly from the rear wall of the housing 19 for connection with a source 2% of heating power through a main switch 58 (see FIG. 6), a pyrostat or temperature control panel 59, a rheostat 6439 an ammeter 61 and a circuit breaker 62. A bell or buzzer 63 is provided in a circuit from the control panel 59 to give an audible indication of when the power to the heating units is shut 017. This operation may be efiected in a known manner, as by a relay (not shown) which operates upon the attainment of a selected temperature in the oven and/or upon the elapse of a selected time. Specifically, the oven 33 may operate until heat reflected in pyrostat 59 cuts off the mufile or oven 33 and then rings the bell 63. A pilot light 70 may be disposed in the circuit to be energized through a transformer 77 when the power is on. The thermocouple 44 is connected to the temperature indicator 51 through the control panel 59.

In the present embodiment there is provided a motor driven vacuum pump 65, the motor of which draws power from the power line through leads 66 and 67 and is controlled by a switch 68 which is closed to stop the pump when the bell 63 rings. An indicator in the form of a neon glow lamp 69, is provided across the leads 66 and 67 to show when the motor is on.

There is a vacuum pipe line 71 from the pump 65 to the housing 19, so as to after the door 21 has been closed, remove air from the housing prior to the firing operation. The degree of vacuum is indicated by a gauge 72 on the front wall of the casing 12 and connected to the line 71 by a branch line 73. Another branch line 74 leading to the atmosphere has a control or Vacuum exhaust valve 75 which, when opened, releases the vacuum and allows the door 21 to be opened.

In operation, the control valve 75 is closed, the oven 33 before or after loading with articles to be fired, is slid into the housing 19 until its sockets 52 and 53, respectively, receive the power supply plugs 54 and 55. At the same time the prongs 45 and 46 are received in the socket device 47 to connect the thermocouple to the temperature indicator 51. The motor switch 68 is closed, starting the vacuum pump 65. When the pressure in the housing 19 has been reduced to the desired degree, as when the vacuum gauge 72 indicates about of mercury, the main or power switch 58 is to be closed, the reset button 76 and the breaker 62 are closed and the rheostat 60 adjusted to a desired power input to the heating units 35, as indicated on the ammeter 61.

When the articles in the oven have been heat treated to thedesired extent, the power shuts oif, as by a temperature and/0r time control through the'panel 59, causing the buzzer or bell 63 powered through transformer 77 to operate and the circuit breaker 62 to open, as well as the manual reset by kicking out the reset device or button 76. This circuit breaker acts like a fuse box breaker and the reset device 76 may be like arod with an internal microswitch. When the buzzer 63 operates, the pump is to be shut off by opening the switch 68. The exhaust valve may then be opened, relieving the vacuum and allowing the door 21 to be opened for a removal of the articles after cooling to the extent desired.

It will be apparent from the foregiong that the operator may, pursuant to the invention, provide precisely the desired temperature and vacuum conditions and may readily break or restore the vacuum.

Having now described the invention in detail in accordance with the requirements of the Patent Statutes, those skilled in this art will have no difiiculty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.

I claim:

1. A laboratory furnace device comprising a housing, a door for closing said housing, a latch for holding said door closed, rails in the bottom part of said housing with flanges upstanding from support surfaces thereof and extending from the front to the rear wall of the housing, an oven slideably supported on said rails between said flanges so as to be movable between a position outside the housing and one inside the same, electrical heating position inside of said housing, line means interconnecting said source of potential and said electrical connector means, an air exhaust opening in said oven, a motordriven vacuum pump for exhausting the housing and the contained oven, a pipe line connecting said pump and said housing, and an exhaust valve in said pipe line to release the vacuum when desired.

2. A laboratory furnace as defined in claim 1, wherein there is a lamp to show when the pump motor is energized.

3. A laboratory furnace as defined in claim 1, and further including a vacuum gauge connected to said pipe line.

4. A laboratory furnace as defined in claim 1, and further including a casing enclosing said housing, said pump and said pipe line, operating means on the outside face of said casing to control operation of said pump, a temperature sensor in said oven, a temperature recorder on the outside face of said casing, and means interconnecting said sensor with said recorder.

References Cited in the file of this patent UNITED STATES PATENTS 1 ,907,290 Forde May 2, 1933 2,398,874 Weyhung Apr. 23, 1946 2,636,915 Gold Apr. 28, 1953 FOREIGN PATENTS 838,778 Great Britain June 22, 1960 

1. A LABORATORY FURNACE DEVICE COMPRISING A HOUSING A DOOR FOR CLOSING SAID HOUSING, A LATCH FOR HOLDING SAID DOOR CLOSED, RAILS IN THE BOTTOM PART OF SAID HOUSING WITH FLANGES UPSTANDING FROM SUPPORT SURFACES THEREOF AND EXTENDING FROM THE FRONT TO THE REAR WALL OF THE HOUSING, AN OVEN SLIDABLY SUPPORTED ON SAID RAILS BETWEEN SAID FLANGES SO AS TO BE MOVABLE BETWEEN A POSITION OUTSIDE THE HOUSING AND ONE INSIDE THE SAME, ELECTRICAL HEATING MEANS IN SAID OVEN, PLUG MEANS EXTENDING REARWARDLY FROM SAID OVEN, A SOURCE OF ELECTRICAL POTENTIAL LOCATED EXTERNALLY OF SAID HOUSING, ELECTRICAL CONNECTOR MEANS 